Distorter Characterisation Using Mutual Inductance in Electromagnetic Tracking

Measuring the Canopy Architecture of Young Vegetation Using the Fastrak Polhemus 3D Digitizer

In the context of climate change conditions, addressing the shifting composition of forest stands and changes in traditional forest management practices are necessary. For this purpose, understanding the biomass allocation directly influenced by crown architecture is crucial. In this paper, we want to demonstrate the possibility of 3D mensuration of canopy architecture with the digitizer sensor Fastrak Polhemus and demonstrate its capability for assessing important structural information for forest purposes. Scots pine trees were chosen for this purpose, as it is the most widespread tree species in Europe, which, paradoxically, is very negatively affected by climate change. In our study, we examined young trees since the architecture of young trees influences their growth potential. In order to get the most accurate measurement of tree architecture, we evaluated the use of the Fastrak Polhemus magnetic digitizer to create a 3D model of individual trees and perform a subsequent statistical analysis of the data obtained. It was found that the stand density affects the number of branches in different orders and the heights of the trees in the process of natural regeneration. Regarding the branches, in our case, the highest number of branch orders was found in the clear-cut areas (density = 0.0), whereas the lowest branching was on-site with mature stands (density = 0.8). The results showed that the intensity of branching (assessed as the number of third-order branches) depends on the total number of branches of the tree of different branch orders but also on stand density where the tree is growing. An important finding in this study was the negative correlation between the tree branching and the tree height. The growth in height is lower when the branching expansion is higher. Similar data could be obtained with Lidar sensors. However, the occlusion due to the complexity of the tree crown would impede the information from being complete when using the magnetic digitizer. These results provide vital information for the creation of structural-functional models, which can be used to predict and estimate future tree growth and carbon fixation.

Magnetic Tracking System for Heart Surgery

Cardiac ablation is a minimally invasive, low risk procedure that can correct heart rhythm problems. Current techniques which determine catheter positioning while a patient is undergoing heart surgery are usually invasive, often inaccurate, and require some forms of imaging. In this study, we develop a unique real-time tracking system which can track the position and orientation of a medical catheter inside a human heart with fast update rate of 200 Hz and high precision of 1.6 mm. The system utilizes a magnetic field-based positioning method involving an efficient solution algorithm, new magnetic field detection hardware and software designs. We show that this type of positioning has the benefits of not needing a line-of-sight between emitter and sensor, supporting a wide dynamic range, and can be applied to other medical systems in need of real-time positioning.

A Radiolucent Electromagnetic Tracking System for Use with Intraoperative X-ray Imaging

In recent times, the use of electromagnetic tracking for navigation in surgery has quickly become a vital tool in minimally invasive surgery. In many procedures, electromagnetic tracking is used in tandem with X-ray technology to track a variety of tools and instruments. Most commercially available EM tracking systems can cause X-ray artifacts and attenuation due to their construction and the metals that form them. In this work, we provide a novel solution to this problem by creating a new radiolucent electromagnetic navigation system that has minimal impact on -ray imaging systems. This is a continuation of our previous work where we showed the development of the Anser open-source electromagnetic tracking system. Typical electromagnetic tracking systems operate by generating low frequency magnetic fields from coils that are located near the patient. These coils are typically made from copper, steel, and other dense radiopaque materials. In this work, we explore the use of low density aluminum to create these coils and we demonstrate that the effect on X-ray images is significantly reduced as a result of these novel changes in the materials used. The resulting field generator is shown to give at least a 60% reduction in the X-ray attenuation in comparison to our earlier designs. We verify that the system accuracy of approximately 1.5 mm RMS error is maintained with this change in design.

Planar Body-Mounted Sensors for Electromagnetic Tracking

Electromagnetic tracking is a safe, reliable, and cost-effective method to track medical instruments in image-guided surgical navigation. However, patient motion and magnetic field distortions heavily impact the accuracy of tracked position and orientation. The use of redundant magnetic sensors can help to map and mitigate for patient movements and magnetic field distortions within the tracking region. We propose a planar inductive sensor design, printed on PCB and embedded into medical patches. The main advantage is the high repeatability and the cost benefit of using mass PCB manufacturing processes. The article presents new operative formulas for electromagnetic tracking of planar coils on the centimetre scale. The full magnetic analytical model is based on the mutual inductance between coils which can be approximated as being composed by straight conductive filaments. The full model is used to perform accurate system simulations and to assess the accuracy of faster simplified magnetic models, which are necessary to achieve real-time tracking in medical applications.

Electromagnetic Navigation in Craniofacial Surgery Based on Automatic Registration of Dental Splints

Optical navigation method cannot be used in partial craniofacial surgery due to light blocking. At present, electromagnetic navigation method can be used instead. The occlusal splint obtained from the patient's dental mold is used in the traditional electromagnetic navigation registration. Then, marker points are selected manually for registration through imaging data during the operation, which leads to the deviation of selection. In this study, the self-developed registration software was used to perform automatic registration in the intraoperative registration. Experimental results showed that it has higher accuracy and faster speed, and is suitable for the actual operation process in clinical environment compared with the traditional manual registration.